The present invention relates to the production of glass and particularly to improvements in glass feeders.
A glass feeder is the piece of equipment that is used in the glass industry to transport molten glass from the melting furnace, in which the glassmaking materials (soda ash, silica, scrap, and the like) are melted to form the molten glass, to the forming machines in which the desired glass articles are formed from the molten glass. The fundamental function of this equipment, besides providing a route for the molten glass between the furnace and the forming machines, is conditioning the molten glass, that is, permitting it to take on the appropriate desired viscosity, temperature and mass flow uniformity by the time it reaches the forming machines.
There are a large variety of glass feeders according to size, quantity, and furnace characteristics. The size normally depends on the pull rate (i.e. the rate of production of molten glass) and the type of glass produced. Furnaces equipped with one to five glass feeders are normally found in the industry. Their length ranges from 3 to 15 meters and the width from 0.4 to 1.5 m.
The glass enters the glass feeder in a molten state and must be kept in the molten state as it passes through the feeder. The heat is generally provided by either electric means or fuel combustion. The majority of glass feeders are heated by combustion of air and fuel gas, such as natural gas, LPG (liquefied petroleum gas) or others. In conventional practice, to provide uniform heating several small pre-mixed fuel-gas burners, firing with air at ambient temperature, are installed in the sidewalls of the glass feeder, projecting (and projecting a flame) orthogonally to the direction of glass flow.
To condition the glass, molten glass at a temperature on the order of around 1300xc2x0 C. leaving the furnace enters the glass feeder, and among other things the temperature of the molten glass is reduced in as uniform a way as possible, delivering homogeneous glass to the forming machines.
To reduce the molten glass temperature, cooling air can be injected into the center of the glass feeder. This reduces the temperature where the glass flow is hotter and has the highest velocity, while fuel gas is fired in the orthogonally oriented burners in both side walls where glass velocity tends to be lower and glass tends to be cooler due to heat losses at or through the walls.
The firing and heating by combustion with air provides very low flame emissivity. The burner blocks and feeder roof are designed and built in a way that the heat delivered to these regions is in part directed back to the molten glass, near the side wall, to improve the heating where heat is required.
In addition to inefficient and non-uniform heat transfer, the conventional system has other limitations. The turn down ratio is limited, and possibilities exist of flash back when working with low gas velocities and of flame blow off when working with high velocities.
Prior art attempts to solve these problems have used premixed air-gas burners, installed along the feeder side walls, which produce very short and hot flames. The axes of these burners are orthogonal to the flow direction of the molten glass and are located in a horizontal plane just above the molten glass surface.
These flames release high heat fluxes over the glass surface near the side walls as an attempt to gather higher flame temperatures in these regions. This lowers the shear stresses in these zones of glass flow responsible for defects in the end product.
Other attempts to improve glass feeder performance have been in new burner block and roof designs, to improve heat transfer to the glass closer near the side walls.
Thus, there remains an unmet need for techniques that achieve better, more uniform temperature distribution along cross sections of a molten glass feeder, so that the glass temperatures close to the side walls of the feeder are as equal as possible compared with those in the middle of the glass flow, for all horizontal axes in the same cross section, so as to provide better temperature performance of the forming machines and better quality in the end-products.
One aspect of the present invention is a glass feeder comprising
(A) a floor, a pair of opposed side walls, a pair of opposed end walls, and a roof, which together define an enclosed chamber, inlet means in one end wall for receiving molten glass into the chamber, and outlet means in the other end wall or floor for discharging molten glass from the chamber,
(B) at least one burner passing through each side wall, through a burner block, into the chamber, each burner comprising first and second burner head means for combusting oxidant and fuel within said chamber, means for feeding fuel from outside the chamber through a first set of one or more openings in each of said first and second burner head means from within said burner head means into the chamber, and means for feeding oxidant from outside the chamber through a second set of one or more openings in each of said first and second burner head means from within said burner head means into the chamber so that said fuel and oxidant mix at said burner head means after passing therethrough and do not mix before passing therethrough,
wherein said first and second burner head means are oriented with respect to each other that combustion of fuel and oxidant fed therethrough produces flames at each burner head which extend in axially opposite directions and are oriented such that said flames extend parallel to the side wall through which the burner passes and adjacent to said side wall and to the glass surface.
Another aspect of the present invention is a method for operating a glass feeder, comprising flowing molten glass through a glass feeder having a floor, opposing side walls, opposing end walls and a roof which together define a chamber through which the molten glass flows, providing at least one burner passing through each side wall through a burner block into the chamber, each burner comprising first and second burner head means for combusting oxidant and fuel within said chamber, means for feeding fuel from outside the chamber through a first set of one or more openings in each of said first and second burner head means from within said burner head means into the chamber, and means for feeding oxidant from outside the chamber through a second set of one or more openings in each of said first and second burner head means from within said burner head means into the chamber so that said fuel and oxidant mix at said burner head means after passing therethrough and do not mix before passing therethrough,
wherein said first and second burner head means are oriented with respect to each other that combustion of fuel and oxidant fed therethrough produces flames at each burner head which extend in axially opposite directions, and wherein each burner is oriented such that said flames extend parallel to the side wall through which the burner passes and adjacent to said side wall and to the glass surface,
combusting fuel and oxidant at said burners to produce flames which extend along both side walls at the molten glass surface.